Embodiments of the subject matter disclosed herein generally relate to cam actuated valves used in reciprocating compressors, and, more particularly, to mechanisms for changing, within the time range of a compression cycle, an instant when the cam actuated valve is opened and/or changing a time interval during which the cam actuated valve is in an open state.
Compressors are used in engines, turbines, power generation, cryogenic applications, oil and gas processing, etc., to increase a pressure of a fluid. One particular aspect that has to be considered for compressors used in the oil and gas industry is that the compressed fluid is frequently corrosive and flammable. American Petroleum Institute (API), the organization setting the recognized industry standard for equipment used in the oil and gas industry has issued a document, API618 (whose version as of June 2011 is included herewith by reference), listing a complete set of minimum requirements for reciprocating compressors. Thus, the valves and compressors to be discussed herein are considered to be in compliance with these requirements. In other words, it is believed that valves and compressors used in other industries, e.g., the auto industry, would not be considered by those skilled in the art to be analogous with the valves and compressors used in the oil and gas industry.
Conventionally, the valves used in a reciprocating compressor are automatic valves that are switched between a closed state (i.e., preventing a fluid to pass there-through) and an open state (i.e., allowing the fluid to pass there-through) due to a differential pressure across the automatic valve. Using actuated valves instead of automated valves has the benefit that the clearance volume (i.e., a part of the compression chamber volume from which compressed fluid cannot be discharged) occupied by the valves is reduced compared to the automated valves. However, actuation in these compressors requires large forces, large displacements and short response times, relative to respective ranges of parameters characterizing currently available actuators.
One mechanism that may be employed to provide the required large forces and short actuation times uses cams that are continuously rotated. One problem with this conventional mechanism is that the instant when the valve opens during a compression cycle and a time interval during which the valve is in an open state are fixedly determined based on an angular position and an angular span of the oblong portion of the cam that rotates to cause the displacement actuating the valve.
It would be desirable to provide valve assemblies and methods for cam actuated valves in reciprocating compressors that allow adjusting the instant when the cam actuated valve opens during a compression cycle, and/or a time interval during which the valve is in an open state.